U.S. patent number 4,586,819 [Application Number 06/510,912] was granted by the patent office on 1986-05-06 for laser raman microprobe.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Yoshiaki Hanyu, Yutaka Hiratsuka, Kenji Tochigi.
United States Patent |
4,586,819 |
Tochigi , et al. |
May 6, 1986 |
Laser Raman microprobe
Abstract
A laser Raman microprobe separates a laser beam reflected by a
sample and a Raman scattered light generated by the sample by a
filter which transmits or reflects a light in a predetermined
wavelength region including a wavelength region of the reflected
laser beam and applies only the Raman scattered light separated by
the filter to a single-monochromator for spectroanalysis. A high
sensitivity analysis is attained by the single-monochromator.
Inventors: |
Tochigi; Kenji (Yokohama,
JP), Hanyu; Yoshiaki (Yokohama, JP),
Hiratsuka; Yutaka (Yokohama, JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
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Family
ID: |
27313600 |
Appl.
No.: |
06/510,912 |
Filed: |
July 5, 1983 |
Foreign Application Priority Data
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Jul 9, 1982 [JP] |
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57-118514 |
Oct 6, 1982 [JP] |
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57-174529 |
Dec 10, 1982 [JP] |
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57-215404 |
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Current U.S.
Class: |
356/301;
356/318 |
Current CPC
Class: |
G01N
21/65 (20130101); G01N 2021/656 (20130101) |
Current International
Class: |
G01N
21/65 (20060101); G01N 21/63 (20060101); G01J
003/44 (); G01N 021/65 () |
Field of
Search: |
;356/301,317,318,417,73
;350/166,502,508,509,511,523,524 ;250/459.1,461.1,461.2,458.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0918088 |
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Feb 1963 |
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GB |
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2039031 |
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Jul 1980 |
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GB |
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Other References
Mole Brochure, Instruments SA, Inc. 11/76. .
Zeitschrift fur Wissenschaftliche Mikroskopie, Ploem, J. S., vol.
68, 1967, pp. 129-142. .
"A Laser Microscope," Peppers, N. A., Applied Optics, vol. 4, No.
5, p. 555, 5/65. .
"Raman Measurements of Stress in Silicon-on-Sapphire Device
Structures," Brueck, S. R. and others, Appl. Phys. Lett., vol. 40,
5/15/82, p. 895. .
"A High Frequency Kerr-Effect Microscope for Bubble Devices,"
Harrison, Colin G., and others, IEEE Transactions on
Instrumentation and Measurement, vol. IM-30, No. 3, 9/81, p. 202.
.
"New Developments in Raman Spectrometry," Delhaye, M., and others
Proc. Soc. Photo-Opt. Instrum. Eng., vol. 236, p. 24..
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Primary Examiner: Evans; F. L.
Assistant Examiner: Harringa; Joel L.
Attorney, Agent or Firm: Antonelli, Terry & Wands
Claims
We claim:
1. A laser Raman microprobe for analyzing a sample comprising:
a microscope;
a laser oscillator;
laser directing means for directing a laser beam generated by said
oscillator to the sample through said microscope;
an optical system for passing along at least a portion thereof in
combination both a laser beam reflected by the sample and applied
to the microscope and Raman scattered light generated by the sample
and applied to the microscope,
said optical system including filter means disposed at an angle in
an optical path the reflected laser beam and the Raman scattered
light for separating the reflected laser beam and the Raman
scattered light having wavelengths dependent upon the wavelength of
said laser oscillator; and
a sample analyzer including a single-monochromator coupled to said
optical system for analyzing the sample based on a resulting
spectrum;
said filter means directing the separated Raman scattered light
directly to said single-monochromator.
2. A laser Raman microprobe according to claim 1, wherein said
filter means is a dichroic mirror for transmitting the light in a
short wavelength region including the wavelength region of the
reflected laser beam and for reflecting the Raman scattered
light.
3. A laser Raman microprobe according to claim 1, wherein said
filter means is a band-pass filter for transmitting the light in
the wavelength region of the reflected laser beam and for
reflecting the Raman scattered light.
4. A laser Raman microprobe for analyzing a sample comprising:
a microscope;
a laser oscillator;
laser directing means for directing a laser beam generated by said
laser oscillator to the sample through the microscope;
an optical system for passing along at least a portion thereof both
a laser beam reflected by the sample and applied to the microscope
and Raman scattered light generated by the sample and applied to
the microscope in combination,
said optical system including separation means for separating the
reflected laser beam from the Raman scattered light passed in
combination, said separation means including a plurality of filters
for transmitting or reflecting different wavelength regions of
light, one of said filters being disposed in an optical path of the
combination of the reflected laser beam and the Raman scattered
light for separating the Raman scattered light; and
a sample analyzer including a single-monochromator coupled to said
optical system and analyzing the sample based on a resulting
spectrum;
said one of said filters being disposed for applying substantially
only the Raman scattered light to said single-monochromator.
5. A laser Raman microprobe according to claim 4, wherein said
plurality of filters are dichroic mirrors each for transmitting or
reflecting light in a short wavelength region including the
wavelength region of the reflected laser beam.
6. A laser Raman microprobe according to claim 4, wherein said
plurality of filters are band-pass filters each for transmitting or
reflecting light in the wavelength region of the reflected laser
beam.
7. A laser Raman microprobe according to claim 4, wherein said
plurality of filters include at least one dichroic mirror for
transmitting or reflecting light in a short wavelength region
including the wavelength region of the reflected laser beam and a
plurality of band-pass filters for transmitting or reflecting light
in the wavelength region of the reflected laser beam.
8. A laser Raman microprobe according to claim 4, wherein said
plurality of filters are radially arranged.
9. A laser Raman microprobe according to claim 4, wherein said
plurality of filters are arranged in at least one line.
10. A laser Raman microprobe according to claim 4, comprising light
detection means for detecting the reflected laser beam separated by
said separation means, including an image pickup camera and drive
means for driving said filters so as to successively locate one of
said filters at an angle in said optical path and select a
corresponding one of said filters in response to the maximum image
output from said light detection means to thereby eliminate stray
light due to the reflected laser beam in the Raman scattered light
from the filter at maximum.
11. A laser Raman microprobe for analyzing a sample comprising:
a microscope;
a laser oscillator;
laser directing means for directing a laser beam generated by said
laser oscillator to the sample through said microscope;
an optical system for passing along at least a portion thereof a
laser beam reflected by the sample and applied to the microscope
and Raman scattered light generated by the sample and applied to
the microscope in combination,
said optical system including at least a filter located at an angle
in an optical path of the combined reflected laser beam and Raman
scattered light passed from said microscope for reflecting light in
a predetermined wavelength region and for transmitting light in
another predetermined wavelength region so as to seperate the
reflected laser beam and the Raman scattered light; and
an analyzer including a single-monochromator coupled to said
optical system for analyzing the sample based on a resulting
spectrum;
said filter enabling application of substantially only the
separated Raman scattered light directly to said
single-monochromator.
12. A laser Raman microprobe according to claim 11, wherein said
filter is a dichroic mirror for reflecting the light in a short
wavelength region including the wavelength region of the reflected
laser beam.
13. A laser Raman microprobe according to claim 11, wherein said
filter is a band-pass filter for reflecting the light in the
wavelength region of the reflected laser beam.
14. A laser Raman microprobe according to claim 11, wherein said
filter one of transmits and reflects light in a wavelength region
of the reflected laser beam and one of reflects and transmits light
in a wavelength region of the Raman scattered light, the Raman
scattered light having a wavelength upon the wavelength of said
laser osicillator.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a Raman spectroanalyzer, and more
particularly to a laser Raman microprobe which enables analysis of
a fine sample.
The laser Raman microprobe is disclosed, for example, in U.S. Pat.
No. 4,195,930 to Delhaye et al. In this device, a laser beam
generated by a laser oscillator is irradiated to a sample through a
microscope and a light applied to the microscope, of a Raman
scattered light emanated from the sample and a reflected laser beam
from the sample is split by a splitting prism. One of the two split
components is directed to a screen to display an enlarged image of
the sample on the screen. The other component is directed to a
double monochromator where it is analyzed, and the light is applied
to a photomultiplier to convert it to an electrical signal. By
recording and reading the electrical signal, the sample is
quantatively and qualitatively analyzed.
In this device, in order to perpendicularly irradiate the sample by
the laser beam, a ring-shaped mirror or a disc-shaped half-mirror
is arranged in the microscope. When the ring-shaped mirror is used
a fine sample such as several tens microns or several microns in
diameter cannot be analyzed because a condensed laser beam by the
microscope is several hundreds microns in diameter. On the other
hand, when the disc-shaped half-mirror is used, the condensed laser
beam diameter by the microscope is in the order of 1 micron and a
sample larger than 1 micron in diameter can be analyzed. However,
when the half-mirror is used, the Raman scattered light from the
sample is reduced to one half by the half-mirror and further
reduced to one half by the splitting prism and hence the analysis
sensitivity is lowered. In addition, since the Raman scattered
light as well as the reflected laser beam is applied to the
double-monochromator, the reflected laser beam must be removed by
the double-monochromator and the device is of large scale and
expensive.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a laser Raman
microprobe which can analyze a fine sample with high
sensitivity.
It is another object of the present invention to provide a compact
and inexpensive laser Raman microprobe.
In order to achieve the above objects, in accordance with an aspect
of the present invention, there is provided a filter for
transmitting or reflecting a light in a predetermined wavelength
range including the reflected laser beam in an optical path of the
Raman scattered light and the reflected laser beam transmitted
through the microscope so that the predetermined range of light
including the reflected laser beam and the Raman scattered light
are separated by the filter and the Raman scattered light free from
the reflected laser beam is applied to a single-monochromator to
enable analysis of a fine sample such as foreign matters of 1 .mu.
or less in diameter on an IC wafer with high sensitivity .
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a conceptual view of a laser Raman microprobe for
illustrating a principle of the present invention,
FIG. 2 is a view of a filter of FIG. 1 as viewed in a direction of
an arrow II,
FIG. 3 is a spectrum chart of one example of analysis of a sample
by the laser Raman microprobe of the present invention,
FIG. 4 is a spectrum chart of a comparative example analyzed by a
double-monochromator which is not in accordance with the present
invention,
FIG. 5 illustrates a plurality of filters arranged in at least one
line, and
FIG. 6 illustrates another embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
One embodiment of the present invention will now be explained with
reference to the drawings.
FIG. 1 shows an embodiment of the laser Raman microprobe of the
present invention. In FIG. 1, an object lens 3 is arranged at a
lower end of a microscope 2 which faces a sample 1, and a
half-mirror 4 is arranged above the object lens 3 and a window is
formed at the sidewall of the microscope 2 so as to enable a laser
beam to pass through the sidewall and impinge upon the half-mirror
4. A laser oscillator 5 can change a wavelength of a generated
laser beam 6. A mirror 7 is arranged in an optical path of the
laser beam 6 generated by the laser oscillator 5, and reflects the
laser beam 6 toward the half-mirror 4. A condenser lens 8 is
arranged between the mirror 7 and the half-mirror 4 in the optical
path of the laser beam 6 and condenses the laser beam 6 on the
sample 1 in cooperation with the object lens 3. The mirror 7, the
lens 8, the window and the half-mirror 4 are aligned with one
another. Accordingly, the laser beam 6 generated by the laser
oscillator 5 is reflected by the mirror 7, transmits through the
condenser lens 8, passes through the window, enters into the
microscope 2, reflected by the half-mirror 4, transmits through the
object lens 3 and is focused onto the sample 1. A portion of the
laser beam 6 focused on the sample 1 is reflected by the sample 1
to produce a reflected laser beam 9 and the other portion of the
laser beam 6 excites the sample 1 to generate a Raman scattered
light 10. Light separation means 11 is arranged in the optical path
of the reflected laser beam 9 and the Raman scattered light 10
transmitted through the object lens 3 and the half-mirror 4. The
light separation means 11 comprises a pulse motor 12 and six
filters 14, 15, 16, 17, 18 and 19 supported on a rotary shaft 13 of
the pulse motor 12. The filters 14-19 may be dichroic mirrors or
band-pass filters having different transmission light wavelength
bands, and one of them is disposed to extend across the optical
path of the reflected laser beam 9 and the Raman scattered light
10. The filters 14-19 may be commercially available filters of e.g.
a dielectric-coated glass structure, and are selected to transmit
the predetermined wavelength band including the reflected laser
beam 9. In order to observe the sample 1, observing means 20 is
arranged in the optical path of the reflected laser beam 9
separated by the light separation means 11. The observing means 20
comprises a light attenuating filter 21 for attenuating the
reflected laser beam 9, a condenser lens 22 for condensing the
light transmitted through the attenuating filter 21, a camera 23
and a television receiver (not shown) so that an image of the
sample 1 under analysis is displayed on the television receiver.
The condenser lens 24 is arranged in the optical path of the Raman
scattered light 10 separated by the light separation means 11 to
condense the Raman scattered light 10. A single monochromator 25
has its inlet slit 26 arranged at a focal point of the condenser
lens 24. Arranged in the single monochromator 25 are a first
collimator 27 for reflecting the Raman scattered light 10 inputted
from the inlet slit 26, a diffraction grating 28 which receives the
Raman scattered light 10 reflected by the collimator 27 and
produces spectra thereof, a second collimator 29 for reflecting the
spectra from the diffraction grid 28 and a reflection mirror 31
which reflects the spectra from the collimator 29 toward an outlet
slit 30. The diffraction grating 28 is rotatably supported in the
single monochromator 25 and rotated by a drive mechanism not shown.
A photomultiplier 32 is mounted to face the outlet slit 30 of the
monochromator 25 and receives the spectra from the monochromator 25
and converts them to an electrical signal. An amplifier 33 is
connected to the photomultiplier 32 and amplifies the electrical
signal supplied from the photomultiplier 32 to a desired level. A
recorder 34 is connected to the amplifier 33 and records the
electrical signal supplied from the amplifier 33.
In the above arrangement, the sample 1 is positioned at the
focusing point of the object lens 3 of the microscope and the
wavelength of the laser beam generated by the laser oscillator 5
and the filter 14 to be used are set.
The laser oscillator 5 is activated to generate the laser beam 6.
Thus, the laser beam 6 is reflected by the mirror 7, transmits
through the lens 8, enters into the microscope 2 via the window,
reflected by the halfmirror 4, transmits through the lens 3 and
focused onto the sample 1. A portion of the laser beam 6 impinged
to the sample 1 is reflected by the sample 1 to produce the
reflected laser beam 9. The other portion of the laser beam 6
impinged to the sample 1 excites the sample 1 to generate the Raman
scattered light 10. Portions of the reflected laser beam 9 and the
Raman scattered light 10 are applied to the object lens 3, transmit
through the half-mirror 4 and impinge to the filter 14. The light
in the predetermined wavelength band including the reflected laser
beam 9 transmits through the filter 14 and the other Raman
scattered light 10 is reflected by the filter 14.
The reflected laser beam 9 transmitted through the filter 14
transmits through the attenuating filter 21 and the condenser lens
22 and enters into the camera 23 so that an enlarged image of the
sample 1 is displayed on the television receiver.
On the other hand, the Raman scattered light reflected by the
filter 14 transmits through the condenser lens 24, is focused to
the inlet slit 26 of the monochromator 25 and enters into the
monochromator 25. The Raman scattered light 10 spectroanalyzed by
the single monochromator 25 passes through the outlet slit 30 and
is applied to the photomultiplier 32 where it is converted to an
electrical signal. The electrical signal is amplified by the
amplifier 33 and then supplied to the recorder 34, which records
the electrical signal.
The positions of the single-monochromator 25 and the observing
means 20, as illustrated in FIG. 1, may be interchanged with the
filter 14 being arranged to separate the reflected laser beam 9 and
the Raman scattered light 10 so that the Raman scattered light 10
is transmitted through the filter 14 and via a mirror 35 through
the condenser lens 24 to the single-monochromator 25 while the
reflected laser beam 9 is reflected by the filter 14 to the camera
23 via the attenuating filter 21 and condenser lens 22 as shown in
FIG. 6.
FIG. 3 shows a spectrum chart obtained for a sample of calcium
carbonate (CaCO.sub.3) having a diameter of 3 .mu.m by irradiating
a laser beam having a wavelength of 514.5 nm to the sample. FIG. 4
shows a spectrum chart for a sample of the same condition but
without filter and with a double-monochromator substantially as in
the above-referenced U.S. patent.
As seen from the composition of FIGS. 3 and 4, an effect of the
reflected laser beam is not observed in FIG. 3 and the analysis of
the light having the Raman shift of 10 cm.sup.-1 is possible. In
FIG. 4, an influence by stray light due to the reflected laser beam
appears in the range of the Raman shift of 100-600 cm.sup.-1 and
the analysis is impossible in the range of the Raman shift of 0-200
cm.sup.-1.
In the present embodiment by the use of the filter 14 (15-19), the
stray light due to the reflected laser beam which cannot be
eliminated by the double-monochromator is completely eliminated
accordingly, an inexpensive and compact laser Raman microprobe can
be provided.
While the six filters 14-19 are radially arranged in the light
separation means 11 in the above embodiment, only one filter may be
arranged or a plurality of filters may be movably arranged in a
line or lines and they may be selectively used.
The filters 14-19 may reflect the light in the predetermined
wavelength band including the laser beam. FIG. 5 illustrates a
plurality of filters 14'-19' arranged in at least one line. In such
arrangement, the filters may be driven in a linear manner in place
of the rotational movement illustrated in FIGS. 1 and 2.
In general, when the laser beam is irradiated to the sample to
generate the Raman scattered light from the sample, an intensity of
the Raman scattered light is inversely proportional to fourth power
of the wavelength of the laser beam (for a given intensity of the
laser beam). Accordingly, in order to intensify the Raman scattered
light, it is desirable to irradiate the sample with a laser beam of
a short wavelength. However, the sample irradiated by the laser
beam absorbs a portion of the laser beam and is heated by an energy
thereof. The absorption of the laser beam by the sample tends to be
larger as the wavelength of the laser beam is shorter accordingly,
if the sample to be analyzed is of a material such as an organic
material which is modified by heat, it is difficult to analyze the
sample by using the laser beam having the short wavelength. Thus,
it is necessary to select the laser beam (wavelength) depending on
the material of the sample to be analyzed. By arranging the laser
oscillator 5 which can generate variable wavelength of the laser
beam 2 and the light separation means 11 having the plurality of
filters 14-19 and linking the laser oscillator 5 to the light
separation means 11, as shown in the embodiment, the laser beam can
be switched depending on the material of the sample 1 and the
analysis is facilitated.
By using narrow band band-pass filters as the filters 14-19 for
separating the wavelength bands of the laser beam, spectra in
shorter and longer wavelength regions than the wavelength of the
laser beam can be obtained. By comparing the spectra in these
wavelength regions, a temperature of the sample under analysis can
be exactly detected. Accordingly, it is possible to determine
whether an amorphous sample has been crystallized during the
analysis and an exact analysis is attained. A relation between a
phase of the sample and the result of analysis is clearly defined
and reliability of the analysis is greatly enhanced.
* * * * *